The present invention relates generally to holographic devices, and more particularly to a method for making multi-layer holograms.
As electronic technology advances there is an increase in demand to incorporate graphic displays into a variety of products. Color graphic displays are typically based on miniature liquid crystal displays on silicon substrates. The displays are typically monochromatic. Color imagery is generally provided by multiplexing of the additive primary colors red, green, and blue. In temporal multiplexing colors are sequentially switched between the three primary colors and if the switching rate is fast enough, the eye temporarily integrates the three images to form a single full color image. In order to modulate the intensity of each color, a color filter is typically combined in series with a display capable of generating a gray scale which is synchronized with the color filter. As new technology provides smaller display panels, there is a problem of magnifying the tiny images displayed on the display chips to give practical fields of view. Conventional optical solutions are generally large and cumbersome. Holographic optical elements, which are intrinsically thin and light weight, offer a solution for many applications such as wearable displays. Since holographic optical elements are intrinsically narrow band devices, color imaging applications require the use of separate red, green, and blue holographic optical elements stacked together. The stacking of holographic optical elements, however, presents a major optical alignment problem.
A color display may also be formed with a microdisplay and a holographic optical element comprising three separate holographic layers, each layer sensitized to one of the primary colors. Each layer is typically produced individually and the layers are stacked together to form the holographic optical element. Since the holograms are formed separately in each layer, the layers must be properly aligned when the layers are stacked together to form the holographic optical element. Improper alignment of the layers may result in poor image display.
There is, therefore, a need for a method for producing efficient multi-layer holograms which eliminate the need to align individually created holograms.